Alpha-1-antitrypsin (AAT) is the major proteinase inhibitor in human sera. The most common form of this glycoprotein (i.e., the homozygote MM phenotype), as well as the homozygote ZZ phenotype which is associated with chronic obstructive lung diseases, have been purified using classical chromatographic procedures. Spectral studies will be used to study both native and chamically modified AAT from each of these variant forms. These studies include ANS-dye binding studies to probe for hydrophobic sites using fluorescence spectroscopy, and polarization fluorescence spectroscopy to study kinetic and thermodynamic interactions of AAT with various other proteins (enzymes, zymogens, etc.). In addition, we are using chemical modification of methionine residues to study both the mechanism of inactivation of AAT by oxidants, as well as the topology of both the M and Z forms of the protein, and chemical modification of the labile disulfide bond of AAT, in order to ascertain its function. Finally, using C14-containing diisopropyl fluorophosphate, a study has been initiated on the proteases in normal and diseased individuals. These investigations are aimed at a better understanding of the chemistry and physiology of AAT.